With point to point links (e.g., in chip to chip communications), as data rates increase, inter symbol interference (ISI) can become more problematic due, for example, to channel bandwidth limitations. With ISI, timing uncertainties can increase resulting in higher bit error rates for recovered data. To reduce ISI, a high-pass filter (either in the transmitter or receiver) may be used to equalize the low-pass behavior of a channel for a given data rate. In some applications, high-pass filters may be used to insert a zero, for example, in a receiver side amplifier.
With active equalizers, the zero frequency can be adjusted in order, e.g., to adjust for different data rates. However, it may be desirable to be able to have more adjustment capability, e.g., to equalize for channel variations. Other issues with receiver side equalizers may also be considered. For example, with a differential equalizer, it may be desirable to be able to adjust the offset between the differential signals.